This invention relates generally to navigation aiding systems, and particularly to a system for radio navigation and positioning on and above the Earth's surface by using the redundant component waveforms of television signals for hyperbolic radiolocation when television signals are synchronously transmitted. The inherent timing accuracy of television signals, specified and controlled by strict technical standards, is an important element in contemplation of the non-dedicated navigational system.
The navigation and positioning of sea, land and airborne vehicles and even of individual persons is a continuing problem to which continuously improved solutions have been sought and found since and even prior to the invention of the astrolabe. Particular challenges to the state-of-the-art include, but are not limited to, navigation of ships in shoal waters, congested harbors, and in search of (or returning to the sites of) mineral deposits on or below the sea floor; the navigation of aircraft during departure, enroute and arrival operations; the navigation and positioning of survey parties carrying instrumentation in vehicles, with beasts of burden or by man-pack.
A significant problem in the practice of modern electronic navigation is that, with the exception of low accuracy radio direction finding methods, all radio-based navigational systems require the establishment of dedicated transmitting stations which are expressly configured for the navigational purpose, although some systems admit of use for secondary purposes. Illustrative of systems which depend upon the use of dedicated transmitters are such public systems as Loran, Omega and Transit, and such private systems as are established to serve the needs of a small group of users, usually in a particular geographic area and generally on non-permanent basis, for example as LORAC, RAYDIST and HIFIX.
Among the earliest significant steps in the evolution of radiolocation systems were the demonstrations circa 1902-1905 by G. Marconi of directional antennas. Through use of a directional antenna, such as a loop antenna, as part of the receiving equipment, a navigator could take bearings upon several radio stations whose locations were known and ascertain his own position by triangulation. While the bearing accuracy (thus position accuracy) was generally limited by the physical constraints on portable antennas, the so-called radio direction finding method possessed the advantage of being usable with signals that could be received from any radio station, including commercial radio broadcast stations.
Experiments in 1925 by G. Breit and M. Tuve used radio frequency pulses and their reflections to measure the height of the Kennelly-Heaviside layer. The invention of the radio altimeter followed in 1928. In both the experiments and the invention, the determination of distance was made by measuring the interval between the time a pulse was transmitted and the time the reflected signal was returned and by applying the known velocity of radio propagation to convert the time interval to distance. The same principle is applied in radar, another navigational aid.
The first system widely used to determine the position of an unknown receiving point by the hyperbolic method was Loran, which was substantially developed during World War II. Present day Loran-C, Omega and many other navigational systems depend for their operation on evolutions of the basic hyperbolic method in which differences in the time at which signals from a number of transmitters at known locations are received at an unknown point may be used to construct (on charts or, contemporaneously, through computer processing of the interval and other data) hyperbolic lines of position the intersections of which define the unknown location.